This invention relates to a bicycle rim having a brake track. More particularly, the bicycle rim includes non-random surface features in the form of directional grooves.
Bicycle wheels and rims have been in use for well over a century. Historically, bicycle rims have been made of wood, steel or aluminum. However, some bicycle rim manufacturers have begun to produce bicycle rims of other materials, such as lightweight fiber-reinforced plastics (FRPs), including carbon fiber, fiberglass, and/or nylon fibers, for example, that are mixed in a curable resin such as epoxy-based resins, phenolic-based resins and/or ester-based resins. Of these composite rims, some have been made entirely of FRP composite materials (“full composite wheels”), whereas others have incorporated components of different materials in addition to FRP composites (“multi-component rims”).
Carbon fiber rim brake surfaces are difficult to design. Early carbon rims used the molded surface of the rim structure itself as a brake track or braking surface, which was generally troublesome since the as-molded rims typically had a thin layer of mold release embedded in the surface, the presence of which was not suitable for braking since mold release materials yield a low coefficient of friction. Mold release is used to ease the removal of the rim from the mold during manufacturing. After a short period of brake use, the mold release and outer layer of epoxy on the rim is worn away, exposing the vulnerable carbon fiber beneath. It is easily understandable why it is disadvantageous to wear down and/or break the structural carbon fibers of the rim, because over time the rim is gradually weakened. Carbon surfaces are relatively poor at resisting wear and can provide poor frictional performance, especially when wet. Thus, carbon fiber surfaces are generally unsuitable as brake tracks for FRP rims.
Later rims use fiberglass, quarts fiber, or Kevlar fibers in the brake track area of the rim or as an additional structure positioned on top of the structural rim material to form a brake track. These materials are considered to have better wear characteristics than carbon and provide varying degrees of improved braking performance.
One approach to provide a brake track involves the addition of a veil of silicon carbide fibers and/or micro-beads or micro-particles alone or in combination or mixed with glass in the brake track. The silicon carbide fibers are harder than glass and offer significantly improved wear performance as well as brake ‘feel’ but are very expensive and difficult to work with due to high fiber stiffness. The addition of silicon carbide fibers can add considerable manufacturing cost to the rim. While modern aircraft and auto racing brake rotors are currently being made from silicon carbide fibers, these materials are currently quite expensive, hard to process and are difficult to form into smaller radii structures, such as for a bicycle rim, especially in a manufacturing setting. This lack of pliability limits their application to rim design and potentially prohibits use for certain complex rim shapes. On the other hand, silicon carbide micro-beads have recently been used successfully in brake tracks.
Some rim manufacturers have experimented with post-applied ‘ceramic’ brake track coatings. These range from painted-on applications that are heat cured, to plasma-sprayed coatings. All of these coatings offer aggressive frictional surfaces but suffer from being very brittle, heavy and generally requiring high temperature application procedures that can damage the molded rim. These coatings also suffer from geometric application issues, since being post-applied, the brake surfaces are inherently imperfect and non-parallel due to lack of geometric control.
There is a demand, therefore, to provide a bicycle rim with a durable and cost-effective brake track with excellent braking characteristics. The invention satisfies the demand.